Kids party question, how do I do this without being rude?

DS is having a Sunday party from 4pm-6pm. He's invited 20 friends. The party is being held in front of our apartment in a game truck. It's this huge pimped out RV for gamers filled with big screen TV's and all the latest video game crap.
There are a few issues though. I live in a tiny apt. No way do I have room for 20 sets of parents. Do parents stay for fourth grade parties?
We only have the RV for two hours (it's expensive) and no food, or drink allowed. I don't want to waste the kids gaming time by dragging them in for cake. And again the space problem.
Originally I thought I'd just set up a table with drinks and snacks, and let them know it's available if they want to grab something. I'm sure they will be in and out using the restroom.
It's just now occurred to me that if I do that, then what the heck do I do about DS opening gifts?
Grrr, I'm a rotten planner with little time left. Please help.

-- You do have to have cake at a birthday party, and you also have to have presents opened. If you have the RV for two hours, can't you just usher everybody inside at the end of the two hours for cake and gifts, and then out they go?

Send them home with cupcakes.
I don't think the parents will stay.
And I'm sure they would rather play in the truck than watch open gifts, so I wouldn't worry about that.
I just heard of that game truck recently, it sounds awesome!

Ugh. DD went to a birthday party this past weekend that was from 4 to 6 and the only food served was ice cream cake. I thought that was so weird since it was clearly during dinner hours. I cannot imagine serving only cake and can doubly not imagine serving nothing.

We had a party at Build a bear and they allowed no food/drinks in the store. So I gave out bags with a cupcake, bottle of water and a snack, Teddy grahams and pirate booty for the gf girl. We didn't want to try to get tables at the food court so that was the alternative. Oh and we didn't open gifts at the store either.

I see no problem with a table with snacks and drinks but you really need to do some kind of cake. You also don't have to open the presents at the party.

Parties around here typically (always in my experience) include a meal, cake, and gift opening. I think after or before the two hours in the RV, you need to serve some $5 pizza, cake, and open presents.

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I like to think the automatic soap dispenser is just really happy to see me.